Myth Busting - Engine Inop Performance

[avbug]

I don't know about this deeply scientific mythbusting effort, but I always demonstrated to students the difference so that they could see for themselves...and there is a difference (not to shoot down your mythbusting effort, here, but it's crap).

As for banking into the good engine being part of a "new" thing wrought on by the FAA...it's in my 60 year old wwii airplane manuals for the airplanes I used to fly...and guess what? It made a big difference.

Lose an outboard engine on a B-24, and without rudder trim, it's about 70 lbs of force on the rudders to hold it. Take out the force with trim, bank into the good engine. Follow the checklist. Clean it up. Then try running it level and ball in the center, vs. not. Dang skippy there's a difference.

 

[skiddriver]

I just pulled out my test cards from my asymmetric flight ride at USNTPS in a U-21. The aircraft was partially instrumented (including a sideslip meter), and we took data to develop static and dynamic Vmc as well other asymmetric flight data.

If the rudder pedals hit the stop before stall/stall warning, we continued to slow the aircraft with 5 degrees of bank into the live engine until we hit a test limit. It gave you a significant difference in Vmc (as we were all taught). Relative climb performance difference wasn't huge, but it was measurable during our tests, which were of course greatly aided by the direct sideslip readout in the cockpit.

 

[UndauntedFlyer]

Let’s talk more about the zero sideslip performance enhancement technique that this thread addresses. First the point is not that it doesn’t exist, the point is that it is so small that it might as well be just an academic point. Just as it would be for a single engine airplane with the ball centered vrs. off by one-half a ball width. As was mentioned in the original posting, how much performance could really be lost in a single engine airplane with a half-ball deflection of the ball in a forward slip? Some for sure, but not really enough to see in the airspeed or rate of climb indicator. So that’s academic too and the degradation in performance would be equal, and neither can be seen.

As was mentioned previously in the original post, I have personally never been able to see any change in performance in a twin engine airplane with an engine feathered and the ball centered vrs. the ball out of center by half a ball width while in the so called zero side slip configuration. I have done this many times in many GA airplanes and have even used a yaw string to see if there is any noticeable deflection with the ball centered or off by half a ball. No change in yaw string deflection is seen. Oh sometimes I hit a slight up draft and the VSI goes up a bit for sure, so I think I have proven the concept correct, but with patience the real result is nothing, no performance enhancement. Time and time again the result is the same. So what can I think when someone reports an increase of 300 – 500 fpm, this must be placebo effect. Maybe there really is a 5 - 25 fpm increase but I can’t read that. And when someone reports that this is in some kind of official book somewhere then that’s fine, after all I have said that it’s in the current FAA Airplane Flying Handbook. But you see, that stuff is all academic. The actual significance and the truth of all this is in real in-flight tests. That’s where the rubber meets the road.

Now if you do this test yourself, you must use real feather because so called zero-thrust settings are all questionable. The only real zero thrust is FEATHER. I say this because, as I said before, here too is where the rubber meets the road.

So in reality does it hurt anything to put in only enough rudder to bring the ball to a half-ball deflection zero side slip configuration? For performance, certainly not, and it’s easier on the leg (or the trim) for a 100 mile diversion to an alternate airport. Plus I suppose the airplane might get an extra mile or two in range. And further, if you lost an engine on takeoff and wanted to take it easy on your leg for the climb out, let off on the rudder a little to half a ball width deflection, using a little bank to correct instead. You certainly won’t hurt performance by this technique, but as for rate of climb enhancement, don’t count on really getting much of anything. Academically yes, less leg muscle yes, but as for performance and safety: It won’t hurt performance and safety is not a concern unless you get too slow and stall cross controlled as it would be with the ball deflected. Remember the wing in a stall always drops opposite the ball and the further the ball is out the harder it drops.

So what is the problem if everybody just believes in this great boost in performance from zero side slip and always just configures to keep the ball out of the center following and engine failure. One thing is mis-identification of a failed engine. I have seen multiengine pilots in training and on check rides try to determine the inoperative engine with the ball out of center. This just doesn’t work for 100% accuracy. To use the “dead foot, dead engine” technique the ball must be centered. Otherwise, as I have see done, confusion causes some pilots to correct for the failed engine with all aileron and the wrong rudder. This can happen, believe me. In this case the dead foot is not the dead engine. If the ball is checked for center position that would show the mistake. So before the student shuts down the wrong engine I ask why the ball isn’t in the center? And the answer is that it’s wrong to have the ball in the center with an engine failure. This is a case of too much cool-aid. I have also seen multiengine students trying to fly single engine instrument approaches in a ball deflected forward slip because of their mis-understanding of the entire reason for the zero side slip concept. They think that having the ball centered with an engine out is never correct. My God, what are they thinking, we are going down hill on the ILS with only partial power on the operating engine. Again, way too much cool-aid here.

Regarding just when all this zero slide slip information started, I really can’t say for sure. If it is in a B-24 manual that’s great because it should be for those guys. I’m sure that if an outboard left (critical) engine was inoperative and particularly if it couldn’t be feathered, the zero side slip would, as I have mentioned, increase the range somewhat. But I can say, as I said in my original post, 30 - 40 years ago, no POH or FAA publication for GA training that I know of explained the zero side slip configuration.

You see, this all came about after a rash of twin training accidents in the 1965- 1975 time period. During that time and before many things were different on multiengine flight training and practical (flight) tests. For example:

• Single engine stalls were trained and tested.
• Fully configured gear and flap down single engine go-around procedures were trained and tested.
• Vmc demonstrations were much more aggressive than they are now. Vmc demonstrations were continued until the pilot was actually losing control.
• There were NO twin engine airplanes with a counter-rotating right engine.

As you might expect there were training accidents. And in particular there were the most training accidents in the newly introduced Twin Comanche. There were also too many accidents in the Beech Barons. Both of these airplanes have higher wing loading than the Apache which was the twin engine training standard at that time. As a result, the single engine stalls and the Vmc demonstrations in these airplanes sometimes got ugly. Because of the higher wing loading the wing would drop hard in the stall and the operating engine would flip the plane inverted into a near inverted spin. Quick and appropriate action most often would save the day, but sometime things just went too far too fast. Way too many training accidents were occurring and finally, the son of a government VIP was killed in a Twin Comanche accident. As a result a somewhat large investigation was ordered by the FAA.

The FAA had a big meeting in Washington and everyone who they though knew anything about multiengine flying was invited to attend. They didn’t know about me then so I wasn’t asked, but I’m told that there were FAA folks, authors, college Phd’s, and manufacturing test pilots from Cessna, Beech and Piper. Everybody wanted to put forth their two-cents worth as to how to stop the accidents. Everyone wanted to make a name for themselves in front of all the FAA big wigs. The conclusions were:

• No more single engine stalls.
• No more Vmc Demonstrations if Vmc is close to Vso except by blocking rudder pedals and then recovering at first indication of a stall, such as the horn.’
• No more single engine go-arounds.
• Vmc was raised on the Twin Comanche with a red paint brush on the airspeed indicator. This was by the power of an FAA AD note.
• Manufactures were encouraged to get a counter-rotating engine for the right side to lower Vmc and eliminate a more critical engine left engine.
• And the “zero side slip” technique was to be taught.

Now I have been told that the college professor, you know the Phd with no multiengine time, is the one that put in his two-cents worth about the zero side slip. He got up in front of everyone with all kinds of charts and graphs to explain the zero side slip technique and then he went on an on until everyone’s eyeballs were spinning. The conclusion was this must all be true, as I agree that it is. My disagreement in this thread is simply with the amount of performance enhancement. They said 300-500 feet per minute and I say no way. Try almost nothing based on my tests only. Some planes may produce more of a performance enhancement but I would be skeptical. There is some, but just as it is in a single engine airplane with the ball centered vrs. off to the side by a half- ball width, it’s just the amount performance change that we are discussing here.

Your comments/questions are welcome.

 

[avbug]

Just one question, really.

Were you born yesterday?

 

[100LL... Again!]

I'm sure it varies a fair bit between different airplane types.

One thing is for certain - the idea that 5 degrees is always the correct amount for max climb is laughable.

 

[UndauntedFlyer]

The thing that I believe is most laughable is the pilot that is flying his final approach single-engine in a twin and trying to hold the ball out of center with rudder and some degree of opposite bank, in other words, in a forward slip.

They think this is the right thing to do for single engine approach safety even though the operating engine is only at about 18"-20" MP and the airplane is holding airspeed and descent rate perfectly.


People like this have been brainwashed with mis-information or as I have previously said, too much cool-aid. It's not their fault though because they are only the product of the instruction they receive and many of the instructors have had way too much cool-aid too.

I do put some blame on the FAA through the PTS for this particular misunderstanding. Under the TASK, "APPROACH AND LANDING WITH AN ENGINE INOPERATIVE," one of the line items or evaluation elements is, "BANKS TOWARD THE OPERATING ENGINE, AS REQUIRED, FOR BEST PERFORMANCE." Of course the misunderstanding here by the student is that best performance isn't necessary unless the power is at maximum full throttle to hold required airspeed and descent profile. So therefore even if the "zero side slip" technique truly did enhance performance, only then with max power set would it be used.


Of course this whole thread disputes the whole zero side slip concept pretty much by saying the performance enhancement are so slight that it's not worth concerning yourself with, at least in most any light twin and its not even a consideration to be discussed in large jets.

 

[nosehair]

this whole thread disputes the whole zero side slip concept pretty much by saying the performance enhancement are so slight that it's not worth concerning yourself with.

...yeah, and what about those people who promote keeping your tires aired up?...yeah, ya might get an extra mile or two gas milage, but..so what?...not what they say about 4 or 5...huh!..(snort)

 

[MauleSkinner]

Of course this whole thread disputes the whole zero side slip concept pretty much by saying the performance enhancement are so slight that it's not worth concerning yourself with.

I beg to differ...if you read my original post

Have you ever tried it in the clouds at 200 feet AGL, from a ball-centered zero climb? I know a guy who swears it makes a noticable difference there

you'd find out about somebody who definitely figures it's worth concerning yourself with.

 

[avbug]

Five degrees is a certification number. It may take more, it may take less. this has always been the case.

Ball out of the center doesn't mean the aircraft is side slipping. Ball out of the center in a bank means the aircraft is banked and traveling straight ahead, with some horizontal component of lift counteracting assymetrical thrust, with a far lower drag penalty than deflecting rudder and aileron to keep the wings level and the ball in the center.

If you don't understand the concept, then you came from a deprived background, or were never fully taught properly, or perhaps were born yesterday.

The amount of bank required may be half a degree, it may be five degrees, it may even be more. Use what is required, when it is required...nothing published should teach otherwise.

 

[minitour]

Ball out of the center doesn't mean the aircraft is side slipping. Ball out of the center in a bank means the aircraft is banked and traveling straight ahead, with some horizontal component of lift counteracting assymetrical thrust, with a far lower drag penalty than deflecting rudder and aileron to keep the wings level and the ball in the center.

Finally an explination that makes sense. Thank you! I just had to "rote learn" it. Now I understand.

...wow...

Ball out for sure.

Thanks again.
-mini